The present invention relates generally to concrete screeding devices, and more specifically to a combined level- and angle-controlling guidance system for portable concrete screeding devices.
Concrete screeds are used in the concrete industry to level freshly-poured concrete (sometimes referred to as plastic concrete). A number of different types of screed are used for various different applications. Typically, automated screeding devices, such as large laser guided mobile screeds and/or truss screeds, are used to level large and easily accessible concrete pours. An example of a mobile screed is provided in U.S. Pat. No. 4,655,633 to Somero et al., and examples of truss screeds are provided in U.S. Pat. No. 4,586,889 to Krohne et al. and U.S. Pat. No. 4,806,047 to Morrison, all of which are incorporated herein by reference. Manually operated lightweight portable screeds, which may be operated by one or two operators, generally are used to level concrete in small or difficult to reach areas, and areas that have physical obstructions such as piping or conduit. An example of a portable screed is provided in U.S. Pat. No. 4,386,907 to Morrison, which is incorporated herein by reference. Portable screeds also may be desirable when the underlying substrate onto which the concrete is being poured is too weak to hold a mobile screed or can not be truss screeded. For example, portable screeds are often preferred when the concrete is poured on elevated decks or when the presence of pipes or other obstructions prevents the use of forms to guide a truss screed.
Modern concrete contractors often are required to meet industry standards for floor flatness and levelness. Typical standards include American Society for Testing of Materials standard E 1155, American Concrete Institute standard #117, and Canadian Standards Association standard A23.1. These standards specify standards for measuring floor flatness (FF) and floor levelness (FL). Floor flatness generally measures the waviness of the floor, and floor levelness generally measures the deviation from a horizontal plane. FF and FL measurements are unitless measurements of relative quality, with higher quality floors having higher FF and FL numbers. The various types of screed provide different quality floors, and those familiar with the art generally regard manually operated portable screeds as being less capable of creating a flat, level floor than automated screeds. Typical manual screeding methods provide FF and FL measurements of 36 and 20, respectively, although with more care (and greater expense), a manual screeding operation may produce floors of FF45/FL30 quality. In contrast, automated screeds typically provide average FL values of approximately 35, and correspondingly higher FF values.
Portable screed users have devised a number of operation methods in efforts to improve the quality of screeding provided by portable screeds. Portable screed operators typically use a laser leveling system to create reference guides in the plastic concrete then attempt to move the screed blade on the guides to produce a flat and level floor. The laser leveling system usually comprises a 360 degree planar reference laser that emits a laser in all directions and a laser receiving eye adjustably mounted on a post. The laser eye indicates whether it is level with, above, or below the reference laser. The laser eye is adjusted on the post so that when the laser eye is level with the reference laser, the foot of the post is at the desired concrete height. The post is then used to establish a number of reference points in the plastic concrete having the desired concrete height. A straightedge, such as a highway level, is used to trowel the concrete between the reference points into parallel guide lanes having the desired height. Once this is complete, the operators position the screed with one end on each guide lane and drag the screed along the guide lanes to level the concrete between the lanes. As the operators move along, another worker may use the laser eye and post to measure the screeded concrete to ensure that it is within tolerances.
This conventional method of operating portable screeds is relatively inaccurate, and is made difficult by a number of factors. For example, the concrete tends to form a roll of grout along the leading edge of the screed blade, obscuring the operators"" view of the guide lanes.
Various other attempts have been made to increase the accuracy of portable screeds by attaching a laser leveling system directly to the portable screed. Typically, such systems have a pair of laser eyes mounted directly to the portable screed so that the operator or operators can continually assess the height of the screed relative to the reference laser during screeding and make adjustments accordingly. Examples of such devices are provided in U.S. Pat. No. 4,752,156 to Owens, U.S. Pat. No. 4,838,730 to Owens, and U.S. Pat. No. 6,089,787 to Allen et al., each of which is incorporated by reference herein. Such attempts to provide more accurate portable screeds have met with disappointing results, and generally have not been successful on the marketplace because they do not provide a substantial improvement in floor levelness and flatness.
Despite their imprecision, portable screeds remain in popular use because they are relatively fast and convenient, and can be used where more accurate screeds can not reach or operate. In some cases, however, a concrete contractor that is using portable screeds may determine that the portable screed is unable to meet the FF and FL requirements for a particular construction job without expensive finishing procedures or multiple screeding attempts. In these cases, the contractor may have to employ a more accurate truss screed or mobile laser-guided screed to meet the average FF and FL requirements for the job. The use of truss screeds and mobile laser-guided screeds is expensive, however, and many contractors can only afford to rent such screeds for particular jobs or for a limited time. Those contractors that can not afford to rent or own the more expensive screeds may be relegated to working on jobs that have less stringent floor quality requirements.
In light of the state of the prior art, a need still exists to provide more accurate portable screeds. Such screeds preferably will allow contractors to produce high quality floors without relying on truss screeds, mobile laser-guided screeds, and other such expensive and cumbersome machinery.
Accordingly, it is an object of the present invention to provide a guidance system for a portable screed having an inclination measuring means for measuring an inclination, an inclination display means for displaying the measured inclination to an operator, a level measuring means for measuring a height relative to a reference signal, and a level display means for displaying the measured height to the operator. The inclination measuring means, inclination display means, level measuring means and level display means are mountable on a portable screed and the inclination display means and the level display means are adapted to be used by the operator to guide the portable screed.
In various embodiments of the invention, the inclination measuring means is a mechanical or electronic inclinometer. In other embodiments, the level measuring means may be a laser sensor eye that receives a signal from a reference laser. One or both of the measured inclination and level may be displayed on an electronic display, which may be remote from the measuring means, may be mounted on a control panel, or may be integrated into a control unit.
In other embodiments of the invention, the guidance system may also include a tilt measuring means for measuring tilt and displaying it to an operator.
It is another object of the invention to provide a method for guiding a portable screed. The method involves measuring a reference inclination of the portable screed, measuring the vertical position of the portable screed relative to a reference plane, controlling the inclination of the portable screed during screeding to maintain the inclination of the portable screed within a desired tolerance of the reference inclination, and controlling the elevation of the portable screed during screeding to maintain the vertical position of the portable screed within a desired tolerance of the reference plane.
It is yet another object of the present invention to provide a portable screed that has one or more blades, one or more handles, one or more inclination sensors adapted to measure and indicate the inclination of the portable screed during screeding, and one or more level sensors adapted to measure and indicate the vertical position of the screed relative to a reference signal during screeding.
In one embodiment, the portable screed is a two-man screed that has two sets of handles. An inclination sensor and level sensor may be mounted proximal to each set of handles.